If a building is only as good as its foundation, then a smartphone is only as good as its app store. Even as manufacturers continue to stack their handsets with YouTube support, instant messaging, and other essentials right out of the box, the features just don’t add up to the amount of capability a phone can take on in the hands of the right developers: You name it, a good smartphone can do it.

The app store you buy into will have a longstanding effect on the way you use your phone – perhaps more than any other feature. But it’s tough to get a feel for every smartphone app store when you don’t get to push a cart down the aisles until you have a carrier contract in your filing cabinet and there’s no turning back.

With that in mind, we’ve gone out and done the legwork for you and compiled a dossier on five of the most popular (and populated) app stores out there. So check out the wares, do your research, and invest wisely, so you know which is worth dialing into.

Apple App Store

Total Apps: 85,000+
Opened: July 10, 2008

The mother of all app stores (it’s now topped over 2 billion downloads) launched in coordination with the release of the iPhone 3G in the summer of 2008 and rode that all-star handset’s rise to popularity in the subsequent year. The explosive sales of the phone combined with its advanced capabilities (like OpenGL support for 3D games) has made it the de facto app store of choice for budding programmers looking to release their creations into the largest pond out there. In fact, it’s less of a pond now, and more like the Pacific.

For consumers, the rampant competition in the app store also makes it one of the most inexpensive to shop. Many basic apps can be had for free, and if a paid app catches your eye, usually the developer offers a free version to give you a taste before you plunk down your bills.

However, the ease of creating apps has also created an abundance of junk apps that clutter up the store, from virtual lighters and shotguns to pandas. Even searching for an extremely niche app, like a blood-alcohol calculator, will turn up dozens of apps to sift through before you find a quality version.

And Apple is notoriously fickle about the type of apps it allows into its walled garden. Apps that simulate shaking a baby to death have slipped through, while South Park and Nine Inch Nails apps have both been denied on the basis of the mature content they serve up.

Extremely tight integration with iTunes allows iPhone users to browse, buy and even rearrange their apps from a desktop computer, rather than doing it all via the phone. The App Store is also the only one on our list that extends to a non-phone: The iPod Touch.